Inductance device



Dec. 24, 1935. w p COTTER ET AL, 2,025,093

INDUCTANCE DEVICE Filed Oct. 26, 1952 ATTORNEY Patented Dec. 24, 1935UNITED stares FATi'i'i FFEQE field, Mass Bosch ration of New Yorkassignors tion, Springfield, ltiiass, a corpoto United AmericanApplication October 26, 1932, Serial No. 639,599

3 Claims.

This invention relates to improvements in inductance devices, and moreparticularly when employed in the low pass network of a radio powersupply unit, as a eactor.

The object of this inventn is to provide a reactor which automaticallyassumes a maximum value of apparent inductance over a wide range ofdirect current through the reactor.

Another object of this invention to provide an inductance whose valueremains more nearly constant under a direct current flow of widevariation.

Another object is to enlarge the direct current carrying capacity orrating of an inductance without havin the value thereof drop to a pointso low that it becomes useless as a filter element in radio powersystems.

Still a further object is to provide an inductance having rigid elementsbut with a core so designed to present the effect of having a variableair gap, which changes .vith the degree of core saturation.

Other objects and improvements will become apparent when the followingdescription is read in view of he drawing and diagrams in which:

Fig. 1 shows a side elevation of an inductance device according to ourinvention; Fig. 2 is a side view of same; Fig. 3 is a diagram showingthe variation of effective A. C. inductance value with the load current;and Fig. t presents an outline of one method of using our invention.

The same numerals identify the same parts throughout.

It is well known in the art that reactors may be designed for efiicientoperation at specified values of direct current in the winding. Forexample, an iron core reactor may be designed with an airgap which willgive a maximum value of apparent inductance at one particular value ofdirect current. However, for lower values of direct current the apparentinductance is not as high as it would be if the airgap were madesmaller. Also for higher values of direct current the apparentinductance is not as high as it would be if the airgap were madegreater.

In this design of radio power supply systems the object desired is toattain stable output voltage under fluctuating current drain and at thesame time maintain the values of the filter elements, or the LC ratiorelatively constant, in order to remove the hum producing fluctuationsof the rectifier output. There is no difficulty in designing aneffective filter section containing the inductance and capacitancenecessary to make it effective at the hum frequency provided the currentdrain from the system is constant. In certain practice the current drainis not constant, for the tubes draw cu rents in proportion to theconstantly fluctuating volume level of the program. This can es achanging direct current 5 through the windings of the inductance orfilter choke, and results in a varying degree of magnetization in thecore thereof. Under severe current conditions the core becomessaturated, the effective reactance of the choke to the A. C. componentof the rectifier output becomes very low, and a poor filter .g actionresults. The effective A. C. inductance of the choke changes with thedegree of magnetic saturation and the net r ult, when combined with afixed amount of c acity, is a circuit in which the element relation andtherefore the filtering effectiveness varies widely.

In lov. pass filters as used in radio power sup ply systems, values ofcapacity and inductance '20 are chosen which will have a cut-off at somefrequency below that of hum. The product of these two factors shouldremain constant in order to retain any given cut-ofi frequency. It isobvious, therefore, that if the value of inductance drops while thecapacity stays constant, the cutoff frequency will be raised and alarger percentof hum component will pass through the filter. We proposeto remedy this state by providing an inductance or choke whose efiectiveA. C. inductance remains more constant under a wide variation in currenthow, and whose general effectiveness does not drop severely whensubjected to heavy current.

To explain the function and utility of the invention reference is firstmade to Fig. 4 wherein l ndicates the primary of an alternating currenttransformer and 2 a vacuum tube rectifier having a cathode 3 and a pairof anodes 4. The cathode 3 is heated by current from a coil 5inductively related to the coil i and one pole of the cathode isconnected to a lead 5. The anodes 4 are each united to a separateextremity of a secondary coil inductively related to the coil l and thenumeral 8 indicates another lead united to the mid-point of the coil 1.In the line of the conductors 5 and H is an inductance 9 according toour invention and the two leads II and 8 are bridged by a condenser it.

To obtain proper filtering and voltage regulation the inductance is madeas shown in Figs. 1 and 2, wherein the numerals i2 and i2a indicate thetwo sides of a magnetic frame having ends l3 and a transverselyextending portion M in the middle which serves as a core for the turnsof a coil l5. The side l2, ends l3 and middle portion I4 are made in onepiece laminations in the form of an E, while the side We which bridgesthe faces of the ends I3 and middle portion i4 is separately constructedand is of variable cross section as indicated in Fig. 2. For example,the side l2a will be of varying width and comprises portions at, b, cand d, the portion (1 making contact with the surface of the ends I3 andmiddle portion it, while the portions or sections 1), c and d, which arerigid with section a, are separated from the terminal face of the ends13 and portion i 4, by air gaps of progressively greater extent. Theentire magnetic circuit of the coil l5 can, of course, be laminated andall of the parts will be rigidly secured to one another. 7

The efiect of a magnetic circuit, such as shown in Figs. 1 and 2, isillustrated in Fig. 3, wherein the curves a, b, c and (1 indicate therelation between the product of the current and number of turns of thecoil to the inductance L for each of the sections a, b, c and d. Thevalues of the effective A. C. inductance L are plotted as ordinates andthe values of the product of the number of turns and current are plottedas abscissas so that it will be seen that the inductance drops as theampere turns increase. The line [6 represents the combined or resultanteffect.

When a small D. C. current is passed through the winding E5, themagnetic fiux is substantially confined to the core section a. When thecurrent is increased, the flux is shifted toward the stepped sections b,c and :1 according to the proportionate current intensity. This actiongives the effect of altering the airgap and the reluctance of themagnetic circuit to suit the needs of the momentary current intensity.Thus the tolerance of the choke to what would ordinarily be overloadcurrents is materially increased, likewise the drop in A. C. inductancevalue usually associated therewith is substantially reduced, and theinductance is maintained automatically in proper relation to the D. C.current flow to produce eificient regulation.

This invention is highly satisfactory in practice, is inexpensive tobuild, and is of smple construction. The performance and characteristicsare certain, and all likelihood of functional derangement is avoided.

While we have shown and described our invention as applied to aparticular system and as embodying the various devices indicated,changes and modifications therein will be obvious to those skilled inthe art and our object is therefore to cover all such changes andmodifications as fall within the true spirit and scope of our invention.

What we claim is:

1. In a radio power supply device, the combination of a rectifier and afilter circuit connected to the output of said rectifier, said filtercircuit including a series connected inductance and a condenserconnected across said circuit at the output side of said inductance,said inductance comprising a winding around a laminated core, said corebeing formed with paralleled stepped airgaps therein of successivelydiffering lengths.

2. In a radio power supply device, the combi nation of a rectifier and afilter circuit connected to the output of said rectifier, said filtercircuit including a series, connected inductance and a condenserconnected across said circuit at the output side of said inductance,said inductance comprising a winding around a laminated core, one sideof said core being formed with paralleled stepped airgaps therein ofsuccessively increas-r ing extent.

3. In a radio power supply device, the combination of a rectifier and afilter circuit connected to the output of said rectifier, said filtercircuit including a series, connected inductance and a condenserconnected across said circuit at the output side of said inductance,said inductance comprising a winding around a laminated core, said corehaving paralleled stepped airgaps of successively increasing extentformed in a horizontal side thereof.

WILLIAM F. COTTER. MARION E. BOND.

